Biopotential electrodes have been used for more than a century to record the electrical potential at the site of the electrode application. The most common electrode is the disc electrode that can be composed of almost any conducting material to promote low impedance and high quality of signal properties. These electrodes are easy to apply as they are either held in place with the conductive paste, glue, or a self-sticking media. They are considered to be an acute electrode as they eventually deteriorate in signal quality as the impedance increases or they become loose and fall off. This type of electrode needs to be replaced, or adjusted every 12-24 hours to ensure signal viability. One of the “best” surface, recording disc electrodes is the silver-silver/chloride type. However, a skill technician must apply the electrode after careful skin preparation. Eventually (usually between 12 and 24 hours), this electrode needs to be tended to, in order to apply more conductive jelly and reestablish a low impedance and signal integrity. The main disadvantages of the surface disc are: it requires placement, fixation and maintenance by a skill technician; it requires maintenance every 12-24 hours; and it is very susceptible to artifact.
Another type of electrode is the subdermal needle electrode, which is usually composed of a solid metal (such as tungsten, stainless steel, platinum, etc.). It can be inserted subdermally and provides an immediate biopotential signal. The quality of the recording is reasonable but they are prone to artifact and usually have high impedance. They are usually considered to be acute electrodes (minutes, hours) as their rigid properties limit their application on freely moving subjects. Their main disadvantages are: they are a rigid electrode that can cause injury; they are prone to movement and other forms of artifact due to the rigidity and high impedance; and they are acute electrodes.
Several years ago, workers in the EMG field used hypodermic needles to insert stainless steel wires into the muscle to permit acute EMG recordings. Later, in a specific application, this technique was modified by Ives and Gloor in 1977 (Ives, J. R. and Gloor, P. New sphenoidal electrode assembly to permit longterm monitoring of the patient's ictal and interictal EEG. Electroenceph. Clin. Neurophysiol, 1977; 42:575-580) to place a chronic sphenoidal recording electrode in order to record the patient's EEG from the area of the mesial temporal lobe. Wyler then further modified this technique as taught in U.S. Pat. No. 4,805,625 (issued Feb. 21, 1989).
The present invention discloses a Ag—Ag/Cl electrode element that can be of any shape or size (solid, stranded wire, ball of pure silver with a silver-silver/chloride coating) depending on the application. Specifically as an example, a multi-stranded, Teflon insulated, silver wire with a silver-silver/chloride recording tip can be placed subdermally at any body location (human or animal) where one desires to chronically record a biopotential. The insertion device, or introducer, can be a hypodermic or sewing needle, split-cannula, a staple, or a suture. As an example, the multi-stranded pure silver wire with a Ag—Ag/Cl recording tip electrode can be placed by hand using a hypodermic needle as taught by Ives in 1977, 1978 and 2005 (Ives, J. R. and Gloor, P. New sphenoidal electrode assembly to permit longterm monitoring of the patient's ictal and interictal EEG. Electroenceph. Clin. Neurophysiol, 1977; 42:575-580; Ives, J. R. and Gloor, P. Update: sphenoidal. Electroenceph. Clin. Neurophysiol, 1978; 44:789-790; Ives, J. R. New Chronic EEG Electrode for CCU/ICU Monitoring. J. Clin. Neurophysiol, 2005; 22:119-123.) and Wyler (supra).